PROLACTIN AND TESTICULAR LEYDIG-CELL FUNCTION - CHARACTERIZATION OF PROLACTIN RECEPTORS IN THE MURINE MA-10 TESTICULAR LEYDIG-CELL LINE

The direct role of prolactin (PRL) in testicular function is still unclear, mostly because of lack of a suitable in vitro model. To establish the suitability of the MA-10 murine tumor Leydig cell line for the study of PRL receptors (PRLR) and effects on steroidogenesis, we initially characterized PRLR on cultured MA-10 cells. The specific binding (B-s) of [I-125]human growth hormone (hGH) depends on time, temperature, and Mg2+ ion and protein concentrations, with absolute specificity for the lactogenic hormones hGH and ovine PRL. B-s is saturable and is to a single class of high-affinity (K-a = 3.6 x 10(9) M(-1)) low-capacity (B-max = 19.5 fmol/mg protein) binding sites. The molecular weight of PRLR, determined by cross-linking to [I-125]hGH, SDS-PAGE and autoradiography, is 35 kDa for the free receptor, suggesting that the short-form PRLR protein, previously described in liver and mammary glands, is that primarily found in MA-10 cells. Thus, the demonstration of specific PRL binding sites on MA-10 Leydig cells, with characteristics similar to primary Leydig cell PRLR, suggests that this cell line can serve as a good model for both the study of PRLR mechanism of action and the role of PRL in Leydig cell function.